Production of texturised yarn

ABSTRACT

A process for the production of texturised yarn wherein thermoplastic synthetic yarn is sequentially stretched and texturised comprising stretching yarn between a feed means and a draw roll and texturising the drawn yarn by the friction false twist principle wherein the draw roll is also the feed means for and controls the tension of the yarn in the texturising zone characterised in that the yarn passes a plurality of times from the draw roll to a separator roll before reaching the heater of the texturising zone and the separator roll acts as a twist damming element which substantially prevents the twist inserted by the texturising unit running back to the draw roll.

United States Patent [1 1 Doschko Jan. 21, 1975 PRODUCTION OF TEXTURISED YARN [75] Inventor: Werner Doschko, Nuuloch am Leaimbach, Germany [73] Assignee: Imperial Chemical Industries Limited, London, England [22] Filed: July 2, 1973 [21] Appl. No.: 375,937

[30] Foreign Application Priority Data July 13, 1972 Great Britain ..32812/72 [52] US. Cl S7/34 HS, 57/157 S, 57/157 TS [51] Int. Cl. D02g l/02, DOlh 1/28 [58] Field of Search 57/1 R, 34 R, 34 HS, 36,

57/51, 51.2, 51.4, 516,157 R, 157 S, 157 MS, 157 TS, 106

[56] References Cited UNITED STATES PATENTS 3,041,814 7/1962 Held 57/34 HS 3,069,837 12/1962 Olson 57/34 HS X 3,178,795 4/1965 Warthen 57/34 HS X 3,645,081 2/1972 Salama 57/34 HS 3,651,633 3/1972 Steinmiller.... 57/157 'IS X 3,729,916 5/1973 Lusk et al. 57/34 HS Primary Examiner-Donald E. Watkins Attorney, Agent, or FirmCushman, Darby & Cushman [57] ABSTRACT A process for the production of texturised yarn wherein thermoplastic synthetic yarn is sequentially stretched and texturised comprising stretching yarn between a feed means and a draw roll and texturising the drawn yarn by the friction false twist principle wherein the draw roll is also the feed means for and,

ll'Claims, 2 Drawing Figures Chidgey et a1. 57/157 TS PRODUCTION OF TEXTURISEDYARN The present invention relates to improvements in or relating to the production of texturised yarn and to an improved apparatus for the productionof such yarn. In particular the present invention is concerned with the production of texturised yarn by a false twist principle in which yarn is sequentially drawn and texturised and is fed directly from the draw zone to the texturising zone and the draw rolls act as feed rolls for the texturising zone.

False twisting is a technique which is used to produce a texturised effect in yarns and a false twist is conveniently achieved by first passing a moving yarn through a region where it is heated to above the second order transition temperature of the material-from which the yarn is made, cooling the yarn and passing the cooled yarn into a twisting device. The twist imparted to the cooled yarn runs back along the yarn in the opposite direction to that in which it is travelling into the heating zone so that the twist is set in the yarn when it moves into the cooling zone and the temperature drops below the second order transition temperature. After the yarn has passed through the twisting device, it is allowed to untwist so that the untwisting of the yarn which has been set in its twisted state results in a texturised or bulked yarn.

Various devices are known for imparting twist to a moving yarn. In one such device the moving yarn is passed around a member which is provided within and rotates with a hollow spindle. In this way twist is inserted in the yarn as it passes through the spindle. This technique is limited in the amount of twist that can be inserted in a yarn travelling at a particular speed as it is only possible to insert one twist for every rotation of the spindle.

Alternative techniques for imparting twist which overcome this limitation use the friction principle whereby the yarn is twisted by contact with a rotating friction surface. The twist devices which use the friction principle generally consist of rotating hollow surfaces with which the moving yarn makes contact. In-

some such devices the yarn passes through the cylindrical body whereas in others the yarn enters and leaves the body from the same side and is held against the friction surface by a yarn guide.

The present invention is primarily concerned with the production of texturised yarn by the friction false twist principle because this allows a greater degree of twist to be inserted into the yarn for a given speed of rotation of the twist bush.

Yarn is generally texturised between two sets of rolls which control the tension and the twist inserted by'the texturising unit runs back along the yarn to the feed rolls. We have found that where the twisted yarn contacts the surface of a roll which controls the tension in the yarn there is a tendency for the torque in the yarn to cause it to move on the roll which can scuff the surface of the roll and can also result in fluctuations in yarn tension as it passes through the texturising'zone as may be observed by an unstable threadline which results in non-uniform yarn. If the roll that feeds the yarn to the texturising zone is also the draw roll the problem can be more acute as tension fluctuations in the draw zone can also occur which further impairs the uniform-- ity of the finished yarn.

It has already been proposed to produce yarn by sequentially stretching and texturising and to provide a pair of nip rolls between the draw roll and the texturising zone to prevent the twist running back to the draw roll. However, in this technique if the nip rolls are to effectively prevent the run of the twist they must grip the yarn and control the tension of the yarn in the tex turising zone and the surface of the nip rolls can become scuffed and tension fluctuations in the draw can still occur.

One further'problem that can occur if the twist in the yarn runs back onto the tension controlling roll is that adjacent strands tend to become intertwined; this prob- I lem has been known for some time and it has been pro posed that it may be overcome by passing the yarn through grooves in the draw roll or by the provision of suitable yarn guides. However, these techniques do not overcome the problem of fluctuation in tension on the draw roll or the scufflng of the roll by the twisted yarn. This problem is more acute when more than one threadline is being processed on the same roll particularly if opposite twist is being imparted to adjacent threadlines.

The present invention therefore provides a process for the production of texturised yarn wherein thermoplastic synthetic yarn is sequentially stretched and texturised comprising stretching yarn between a feed means and a draw means and texturising the yarn by the friction false twist principle as hereinbefore described wherein the draw means of the stretching zone is also the feed means for and controls the tension in the yarn in the texturising zone, characterised in that the yarn passes through the twist damming element as hereinafter described after leaving the draw roll of the stretching zone and before reaching the heater of the texturising zone said twist damming element substantially preventing the twist inserted by the texturising unit running back to the draw roll.

The twist damming element may be of any suitable construction which does not substantially affect the tension of the yarn, for example, the element may be a pin, around which the yarn is wound or may be a system in which the direction of the yarn path is changed more gradually whilst achieving the necessary degree of'twist damming. We havefound that a particularly useful twist damming'element comprises a series of pulleys or pins around which the yarn passes, the rolls or pulleys being positioned so that the yarnis forced to change by at least as it passes around each roll. In many yarn drawing processes the yarn is drawn between a feed roll and a draw roll and at the draw roll the yarn passes several times between the draw roll and an idler roll spaced a little distance from the draw roll. This technique is employed to minimise yarn slippage at the draw roll and thus stablise yarn tension and the principle function of the idler roll (frequently known as a separator roll) is to ensure that the various twists of yarn around the draw roll, do not become intertwined.

- We have found that such a separator roll may readily be used as the twist damming element if the yarn is wrapped around the separator roll after leaving the draw roll for the final time providing of course that the wrap of the yarn is SUfflClCl'lI to arrest the run of the twist. As a further preferrment a groove is formed in the separator roll to take the wrap of the yarn at the position on the separator roll which is to act as the twist damming element.

The process of the present invention may be applied to the production of yarn from any thermoplastic synthetic material which when twisted at a temperature above its second order transition temperature and then cooled whilst in its twisted state becomes set in the twisted state. Examples of such thermoplastic materials include Nylon 6, Nylon 6.6, polyacrylonitrile and thermoplastic polyesters such as polyethylene terephthalate.

In our preferred process the unstretched yarn is first stretched between a feed station which is generally a feed roll and a draw roll, is then fed directly from the draw roll to the twist damming element, then through a heater zone then to the twist device and finally to a take off unit. We prefer that the heater zone comprise a pin heater around which the yarn is wrapped as this ensures quick heating and uniform heat transfer between the yarn and the heater and thus allows higher speed processes to be used. A plate heater may be used but this is not preferred. Where a pin heater is used an additional feature of our invention is to use a twist damming element which can be moved to alter the angle of wrap of the yarn around the heater pin since this allows a convenient way of adjusting the heating, this is particularly useful as it allows ready modification of the process to allow for the production of different types of yarns. After the yarn has passed through the heater it is cooled so that it is cooled when it reaches the twist device, and it may be necessary to provide cooling plates which direct cold air on to the yarn but generally we find that the distance the yarn travels between the heater and the twist device is sufficient to cool the yarn.

After cooling the yarn passes to the twisting device which may be any of the known friction devices for imparting twist to yarns, in particular the twist bushes such as those described in British Pat. No. 1,197,703 or, as is preferred, the device described in our own French Pat. No. 7,207,922. The twist imparted to the yarn by the twisting device runs back along the yarn into the heater zone so that the yarn is twisted when hot and as the hot twisted yarn cools the yarn is set in its twisted state. In a preferred embodiment of the process of the present invention the yarn is withdrawn from the twist device in such a way that it is subjected to an increase in tension between the draw roll and the withdrawing unit which is generally a roller since we find that the use of this embodiment allows yarn with high bulk as indicated by high crimp rigidity to be obtained.

It has already been proposed to withdraw the yarn from the twist device by the same roll as is used as the draw roll of the stretching zone. However, in this previous publication the roll is stepped so that the yarn is withdrawn by the portion of the roll of smaller diameter. We find it particularly convenient to use a similar system with the exception that the yarn is withdrawn by the portion of larger diameter as described in our Netherlands Patent Application No. 7,215,020. This particular technique thus gives an increase in yarn tension between the two portions of the roll and thus increased crimp rigidity of the yarn together with the added advantage that the dual functions of a single roll enables the apparatus to be more compact.

In the preferred embodiment using the stepped roll as both the draw roll and the withdrawing roll for the texturising zone the yarn passes several times between the portion of smaller diameter and the separator roll to ensure substantially constant drawing tension. After leaving the drawing portion of the stepped roll for the final time the yarn passes again to the separator roll where it is wrapped around sufficiently to act as a twist damming element; the yarn then passes to the heater (preferably a pin heater), then to the twist device and back to the portion of the stepped roll of larger diameter. If desired the yarn may pass a plurality of times between this larger diameter portion and the separator roll to minimise yarn slippage at this point. Finally the yarn passes to the wind up.

The yarn is withdrawn from the texturising unit by the wind up and will be untwisted by the action of the twist bush as it runs to the wind up thus producing a texturised yarn. We have found that the process of the present invention enables a yarn of high crimp rigidity and a low shrinkage to be obtained which is particularly important in yarn that is to be processed into goods which are subsequently shaped and also to achieve uniform dye uptake. In particular we have obtained yarn having a crimp rigidity of from 40 percent to 50 percent and have found that the process may be run continuously without adjacent strands of yarn on the draw roll becoming intertwined.

The process of this invention results in a torque yarn since it has been twisted in one direction about its axis although if a torque free yarn is required, the process may be applied to two separate yarns passing through the apparatus in parallel so that they are subjected to equal amounts of twist. These yarns may then be intertwined with their twists in opposite directions to form a torque free composite yarn. This may readily be achieved by drawing and texturising two separate threadlines through the same apparatus each being twisted in opposite directions during the texturising process. The present invention proves particularly useful in this process since without a twist damming element the two yarns which are twisted in opposite directions tend to roll towards each other on the draw roll and frequently snagging occurs and this may be avoided by employing the techniques of this invention.

The present invention also provides an apparatus for the production of texturised yarns by sequentially drawing and texturising yarn comprising feed means for undrawn yarn, means for stretching the undrawn yarn which also deliversthe yarn to a texturising zone, said texturising zone comprising a heater and a yarn twisting element situated so that the yarn passes the heater before reaching the twisting element characterised in that a twist damming element as hereinbefore described is positioned in the yarn path between said stretching means and said heater said twist damming element being such that it arrests the run of the twist but substantially unaffects the tension in the yarn.

As previously mentioned the twist damming element may be any suitable device which prevents the twist inserted by the twisting element running back to the stretching means and we have found that a pin or a system consisting of several yarn guides around which the yarn passes in such a way that the yarn path alters by an angle of at least around each guide is preferable to arrest the run of the twist. In particular we prefer to use a system containing three such guides. Alternatively the yarn may be wrapped around the separator roll associated with the draw roll as it leaves the draw roll so that the separator roll arrests the run of the twist. We also prefer that the heater is a pin heater around which the yarn is wrapped as this allows good heat transfer between the yarn and the heater which enables high speed processes to be used. Furthermore, if a pin heater is used we also prefer that the position of the twist damming element is adjustable to vary the amount by which the yarn is wrapped around the heater thus giving control over the extent to which the yarn is heated.

We have also found that yarn having a higher bulk level may be obtained if the tension in the yarn is increased during texturising as described in our Netherlands Patent Application No. 7,215,020. In such a process we prefer that for the sake of compactness it is the draw roll which also withdraws the yarn from the texturising zone and that the roll be stepped so that the yarn passes around the portion of greater diameter after it has been through the texturising zone thus giving the required tension increase. The twisting element may be any of the well known devices such as twist spindles and friction bushes although we prefer to use a friction bush which allows faster processes and a higher level of twist to be inserted.

FIG. 1 is a diagrammatic drawing of the apparatus used in carrying out the process.

FIG. 2 is a diagrammatic showing of the separator roll provided with grooves.

The present invention is illustrated but in no way limited by reference to the accompanying diagramatic drawing which shows undrawn yarn 1 being delivered to a feed roll 2 from which it passes to the draw pin 3 and thence to the draw roll 5. The draw roll 5 is stepped and the yarn from the draw pin 3 passes to the portion 6 which is of smaller diameter. The yarn then travels to the separator roll 4 and again to the portion 6. The relative speeds of the feed roll 2 and draw roll 5 are adjusted so that the yarn is stretched to the desired extent. After passage around the portion 6, the yarn passes to the twist damming element which consists of the guides 7, 8 and 9 around which the yarn is wrapped. The yarn then passes to heated pin 10 where it is heated to a temperature above the second order transition temperature of the material from which the yarn is made. Next the yarn passes to yarn guide 11 and into the friction twist bush 12. The yarn path between the heated pin 10 and the yarn guide 11 is sufficiently long to ensure that the yarn is no longer tacky when it passes through the guide 11.

In the type of twist bush illustrated, the yarn passes through the bush and is twisted by frictionalcontact between the inner surface of the bush and the yarn; The twist imparted to the yarn runs back along the yarn towards the heated roll 10 so that the yarn is twisted while hot and the twist becomes set in the yarn as it cools. Some twist however passes over' the pin 10 but it is prevented from travelling back to roll 5 because it is wrapped around the rolls 7, 8 and 9. After passing through the twist bush the yarn passes through another yarn guide 13 to the larger diameter portion 14 of the roll 5. From the portion 14 of roll 5, back to the separator roll again, through the yarn guide 11 and is wound up on the bobbin 15 by means of the ring and traveller As may be seen from the drawing the degree to which the yarn is wrapped around the pin heater 10 may readily be altered by adjusting the position of the yarn guide 9. In another embodiment of our apparatus the yarn guides 7, 8 and 9 may be removed and the yarn wrapped around the separator roll 4 immediately before it passes to the pin heater 10. The embodiment of FIG. 2 shows the separator roll 4 provided with a groove 20 and in which no guides 7, 8 or 9 are used.

The present invention is further illustrated but in no way limited by reference to the following comparative examples.

EXAMPLE 1 Two samples of 7 filament polyamide yarn of drawn decitex 22 were texturised using substantially the apparatus illustrated in the accompanying drawing save that in one run the rolls 7, 8 and 9 were not present and the yarn wrapped around the heated pin 10 by 270 whereas in the second run they were present but rolls 7, 8 and 9 were higher than illustrated in the Figure so that the yarn wrapped around the heated pin 10 by 360. In the process the yarn was withdrawn from the texturising zone by the larger diameter portion 14 of the roll 5 at a speedof 680-metres/minute, the diameter of the larger portion 14 being 4.1 percent greater than the smaller diameter portion 6. The twist bush 12 was rotating at a speed of 21,500 revolutions per minute and the pin 10 was held at a temperature of C.

The threadline of the run including the twist trap was observed to be more stable than the process without the twist trap. In addition the portion 6 of the roll 5 was less scuffed over an extended period and less filamenta- 7 tion of the yarn occured. The properties of the two samples of texturised yarn obtained were as follows:

With Twist Trap Without Twist Trap Hot Shrinkage 7.0 7.5

Crimp Rigidity 42 39 Tenacity (pounds/decitex) 4.8- 4.4

Titre (decitex) 21 2] EXAMPLE 2 With Twist Trap Without Twist Trap Hot Shrinkage 5.5 6.0 Crimp Rigidity 42 32 Tenacity (pounds/decitex) 4,4 41 Titre (decitex) 42 42 The hot shrinkage of the yarn is determined by mak- I ing a 1 metre length of yarn that has been stored for at least 24 hours under normalconditions into'a single loop which is subjected to a tension of 18 grams/- decitex and the length of the loop measured (L,). The loop of yarn is then suspended in boiling water for 15 minutes, dried under normal conditions for 24 hours,

re-subjected to a tension of 18 grams/decitex and the length of the loop measured (L The percentage shrinkage is given by L L /L X 100.

The crimp rigidity of the yarn is a measure of the bulk retention of the yarn and is determined by making a loop from the textured yarn and initially hanging a weight of 0.1 grams per denier on the yarn and suspending the weighted skein in water at C for 2 minutes. The length of the skein is then measured. The weight is then replaced by a weight of 0.002 grams per denier and the length of the skein measured under simi lar conditions. The crimp rigidity is the ratio of the length under a load of 0.002 grams per denier to the length under a load of 0.1 grams per denier expressed as percentage.

EXAMPLE 3 The process of Example 1 was repeated using two separate seven filament yarns which were twisted in opposite directions. The guides 7, 8 and 9 were removed and after the yarns finally left the draw roll they were looped around the separator roll 4 in'two grooves one provided for each yarn. It was found that the process could be run smoothly over an extended period of time whereas when this process was operated without the final loops around the roll 4 and without the grooves in the roll the process was frequently interrupted due to snagging of the two yarns as they rolled towards each other on the draw roll.

I claim:

1. A process for the production of texturised yarn wherein thermoplastic synthetic yarn is sequentially stretched and texturised comprising stretching yarn between a feed means and a draw roll and texturising the drawn yarn by the friction false twist principle wherein the draw roll is also the feed means for and controls the tension of the yarn in the texturising zone characterised in that the yarn passes a plurality of times from the draw roll to a separator roll before reaching the heater of the texturising zone and the separator roll acts as a twist damming element which substantially prevents the twist inserted by the texturising unit running back to the draw roll.

2. A process according to claim 1 in which a groove is formed at the position on the separator roll which acts as the twist damming element.

3. A process according to claim 1 in which the yarn is fed directly from the draw roll to-the twist damming element then through a heater zone to the twist device and finally to the take off unit.

4. A process according to claim 3 in which the heater zone comprises a pin heater around which the yarn is wrapped.

5. A process according to claim 4 in which the separator roll can be moved to alter the extent to which the yarn is wrapped around the pin heater.

6. A process according to claim 1 in which the yarn is withdrawn from the twist device by a withdrawing unit in such a way that the yarn is subject to an increase in tension between the draw roll and the withdrawing unit.

7. A process according to claim 6 in which the withdrawing unit and the drawing means are a single roller which is stepped with the portion of smaller diameter acting as the drawing means and the portion of larger diameter as the withdrawing unit.

8. An apparatus for the production of texturised yarns by sequentially drawing and texturising yarn comprising feed means for not fully drawn yarn, a stretching roller for drawing the not fully drawn yarn which. stretching roller delivers the yarn to a texturising zone comprising a heater and a yarn twisting element situated so that the yarn passes the heater before reaching the twisting element characterised in that the roller is associated with a separator roll and the yarn passes a plurality of times between the roller and the separator roll so that said separator roll acts as a twist damming element.

9. An apparatus according to claim 8 in which a groove is formed in the separator roll to take the wrap of the yarn in the position of the separator roll which acts as the twist damming element.

10. An apparatus according to claim 8 in which the heater is a pin heater. 1

11. An apparatus according to claim 10 in which the position of the twist separator roll may be altered to vary the wrap of the yarn around the pin. 

1. A process for the production of texturised yarn wherein thermoplastic synthetic yarn is sequentially stretched and texturised comprising stretching yarn between a feed means and a draw roll and texturising the drawn yarn by the friction false twist principle wherein the draw roll is also the feed means for and controls the tension of the yarn in the texturising zone characterised in that the yarn passes a plurality of times from the draw roll to a separator roll before reaching the heater of the texturising zone and the separator roll acts as a twist damming element which substantially prevents the twist inserted by the texturising unit running back to the draw roll.
 2. A process according to claim 1 in which a groove is formed at the position on the separator roll which acts as the twist damming element.
 3. A process according to claim 1 in which the yarn is fed directly from the draw roll to the twist damming element then through a heater zone to the twist device and finally to the take off unit.
 4. A process according to claim 3 in which the heater zone comprises a pin heater around which the yarn is wrapped.
 5. A process according to claim 4 in which the separator roll can be moved to alter the extent to which the yarn is wrapped around the pin heater.
 6. A process according to claim 1 in which the yarn is withdrawn from the twist device by a withdrawing unit in such a way that the yarn is subject to an increase in tension between the draw roll and the withdrawing unit.
 7. A process according to claim 6 in which the withdrawing unit and the drawing means are a single roller which is stepped with the portion of smaller diameter acting as the drawing means and the portion of larger diameter as the withdrawing unit.
 8. An apparatus for the production of texturised yarns by sequentially drawing and texturising yarn comprising feed means for not fully drawn yarn, a stretching roller for drawing the not fully drawn yarn which stretching roller delivers the yarn to a texturising zone comprising a heater and a yarn twisting element situated so that the yarn passes the heater before reaching the twisting element characterised in that the roller is associated with a separator roll and the yarn passes a plurality of times between the roller and the separator roll so that said separator roll acts as a twist damming element.
 9. An apparatus according to claim 8 in which a groove is formed in the separator roll to take the wrap of the yarn in the position of the separator roll which acts as the twist damming element.
 10. An apparatus according to claim 8 in which the heater is a pin heater.
 11. An apparatus according to claim 10 in which the position of the twist separator roll may be altered to vary the wrap of the yarn around the pin. 